Don’t ever give me a time machine.

If time travel gets invented in the future, we’ll see evidence of it in the present.


Near the end of Back To the Future, Part II, the Dr. Emmett Brown of 1985 meets the Dr. Emmett Brown of 1955. The younger Brown asks the man he doesn’t recognize as his future self for help installing some sort of electrical fixture. The ’85 Brown, despite lecturing Marty McFly for the entire movie about the horrific implications of meddling with past events, gives his younger self some timely advice on his project and engages him in some inane chatter about the weather. The younger Doc doesn’t even hesitate to consider that he’s speaking with himself.

I find this slightly unbelievable, because if I ever got use of a time machine, I’d assume that my future self would be popping up everywhere. I’d look at every event in my life and think it the result of some sort of tinkering by my future self. If I saw somebody in the grocery store with a pulled-down hat, I would assume it’s my future self trying to avoid detection. Hear a sound in the middle of the night? Future self. He has a key.

Running into just one of my future selves at a time would seem rather mild, in fact. I’d expect dozens of myselves roaming around at once. They have unlimited time and can replicate at will.

If time travel is ever possible, it better be the kind of time travel that could more accurately be called world travel, where the traveler travels not through her own time but to another universe—one exactly like the one she just left but with whatever differences she causes… a universe created by her time travel. I hope that’s what we get, because if this is the only universe, there’s not enough room for all of me.

That the universe exists at all is either terrific evidence that time travel will never be discovered in the future, or the exact opposite.

Philosopher Nick Bostrom has argued that we’re likelier than not to be living in a computer simulation. He reasons that, because computer simulations of consciousness will one day be created, then the number of conscious, simulated individuals will dwarf actual people by orders of magnitude. It would follow, then, that because we exist at all, there’s a better-than-not chance that we are in a computer simulation.I)It’s not unlike the ontological argument for the existence of God, which holds that the very fact that we can conceive of God proves his existence. If we can proceed from where we are right now to a point in time at which humans (or whatever succeeds us, be they evolved humans or artificial intelligence) are capable of building simulated consciousness in a computer program, then it doesn’t matter how far into the future from now that happens—it only matters that it will happen at all. So if that technology eventually exists, there’s no way for us to know that we aren’t products of it, and because it can produce so many different universes, the math is on the side of our universe being a simulation.

I see time travel working the same way. If time travel gets discovered 25 million years from now, then the entire history of the universe is open to meddling. But that presumes that time can be interfered with at all. All serious theorists of time travel (And there actually are many reputable scientists who rigorously study the subject.) say that the past cannot be altered. Contradictions are not possible, and you cannot both travel back in time to kill your grandfather, eliminating yourself from existence, and get born and grow up to eventually go back in time to kill your grandfather (That’s the grandfather paradox, which I’ve written about before.). Relatedly, you cannot write a song and then go back in time and teach your younger self to play that song, because that would create what’s known in theoretical physics as a Jinnee—an object with no originII)The name comes from the Quran, where jinn are mystical desert creatures who leave no earthly trace. Jinn are also the source of the English word and concept of genies. (I’ve also written about this before. It’s the predestination paradox.).

A time tourist!

The universe is long, so time travel could be figured out one day. And if that’s the case, then the fact that there’s a universe at all might be the result of time traveler tampering. Like the time traveler whose desperate attempts to prevent an outcome end up causing that outcome, perhaps our existence is the result of a future time traveler’s mistake.

And if time travel gets figured out, then it stands to reason our world is littered with time tourists. People from the future are LARPing around, not worrying about intruding because the laws of physics prevent them from changing the past anyway. They’re just here to observe.

Or, because the universe is long, it could be that eventually we figure out how to alter the past. And if that’s the case, then everything happening right now could be a consequence of future time traveling. Maybe our present was totally different 24 hours ago.

If the past could be changed, then even the most skillful and cautious traveler would eventually fuck everything up. If the past could be changed, there wouldn’t be a universe.

And if the past can be changed, I implore the people of the future not to give me access to time travel. I am generally a careful person, but I drop phones and my car always seems to be leaking a viscous fluid. I cannot be trusted. Do not give me a time machine.

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I It’s not unlike the ontological argument for the existence of God, which holds that the very fact that we can conceive of God proves his existence.
II The name comes from the Quran, where jinn are mystical desert creatures who leave no earthly trace. Jinn are also the source of the English word and concept of genies.